IL-18, initially termed IFN-7-inducing factor (IGIF), is a member of the IL-I superfamily comprised of IL-lalpha, IL- IB, IL-IRa, IL-18 and the recently identified homologues IL-1H1, IL-H2, IL-1H3 and IL-1H4. We have demonstrated that administration of recombinant IL-18 has significant anti-tumor activity in murine tumor therapy models, but with systemic toxicity. In contrast, local intra-tumoral delivery of IL-18 by adenoviral gene transfer resulted in tumor rejection with induction of tumor specific systemic immunity that was enhanced by co-administration of systemic IL-12 without systemic toxicity. The anti-tumor activity of 1L-I 8 gene transfer was conferred in part by NK cells through an IFN-7-independent, but FasL-dependent pathway. We also have demonstrated that intra-tumoral delivery of IL-18 using genetically engineered DC or in conjunction with DC resulted in a more effective systemic anti-tumor response with cross priming and a higher repertoire of CTL epitopes. IL-18 also was able to stimulate both MHC and co-stimulatory molecules on DC as well as enhanced the effect function of DC through upregulation of FasL and TNF. Thus we have hypothesized that IL- 18 acts as a bridge between the innate and adaptive immune response through the direct regulation of NK, DC and T cell function, stimulating NK mediated lysis of tumor cells that then results in induction of CTL through IL-18 stimulated antigen presentation by DC to T cells. Similar to IL-18, we have shown that an intra-tumoral injection of an adenovirai vector expressing the novel IL-1/IL-18 homologue IL-IH4 stimulates a significant anti-tumor response, resulting in induction of specific anti-tumor immunity that is mediated through an IL-12, FasL, and IFN-y dependent, but NKT cell and IL- 18R independent pathways. These results suggest that IL- 1H4, like IL- 18, could play an important role in the link between innate and adaptive immunity and thus may be useful for tumor immunotherapy. The first goal of the proposal is to understand and contrast the mechanisms through which IL-18 and IL-1H4 stimulate both the innate and adaptive immune responses. The second goal is to develop approaches to optimize the systemic anti- tumor immune responses conferred by IL-18 and IL-1H4 gene transfer, both when administered alone and in conjunction with the Thl biasing cytokines IL-12 and the novel IL,12 family members, IL-23 and IL-27 The successful completion of the proposed studies should result in novel, clinical relevant CGT approaches for treating cancer.